Process for preparing highly reactive lead compound particles

ABSTRACT

A PROCESS IS DESCRIBED FOR PREPARING HIGHLY REACTIVE LEAD ALLOYS HAVING A HIGH SODIUM CONTENT ON THE SURFACE AND A LOWER CONTENT BELOW THE SURFACE BY ALLOWING FINELY DIVIDED LEAD PARTICLES HAVING AN AVERAGE PARTICLE SIZE OF BETWEEN 1 TO 300 MICRONS, PREFERABLY 1 TO 40 MICRONS, WITH MOLTEN ALKALI METAL AT ELEVATED TEMPERATURES, I.E., 100 TO 300*C. IN AN INERT GAS ATMOSPHERE. CONTACT OF THE PARTICLES OF LEAD AND ALKALI METAL IN THE PRESENCE OF AN INERT FINELY-DIVIDED SOLID MATERIAL SUCH AS SILICA IS DESCRIBED. THE PARTICLES OF LEAD AND ALKALI METAL ARE ALSO SHOWN CONTACTED IN THE PRESENCE OF AN INERT LIQUID MATERIAL SUCH AS A HYDROCARBON OIL.

United States Patent 3,558,347 PROCESS FOR PREPARING HIGHLY REACTIVE LEAD COMPOUND PARTICLES Robert D. Gray, Gloucester, and Simon E. Mayer, Lexington, Mass., assignors, by mesne assignments, to PPG Industries, Inc., a corporation of Pennsylvania Application June 5, 1968, Ser. No. 749,898, which is a division of application Ser. No. 430,488, now Patent No. 3,442,923. Divided and this application Mar. 13, 1969, Ser. No. 833,215

Int. Cl. C23c 1/10 US. Cl. 117-100 9 Claims ABSTRACT OF THE DISCLOSURE A process is described for preparing highly reactive lead alloys having a high sodium content on the surface and a lower content below the surface by alloying finely divided lead particles having an average particle size of bet-Ween 1 to 300 microns, preferably 1 to 40 microns, with molten alkali metal at elevated temperatures, i.e., 100 to 300 C. in an inert gaS atmosphere. Contact of the particles of lead and alkali metal in the presence of an inert finely-divided solid material such as silica is described. The particles of lead and alkali metal are also shown contacted in the presence of an inert liquid material such as a hydrocarbon oil.

This application is a division of our US. application Ser. No. 749,898, now US. Pat. 3,472,637 which was a division of US. application Ser. No. 430,488, now US. Pat. 3,442,923.

This invention relates to novel reactive lead compositions and to processes for preparing the same, especially lead-sodium compositions. The invention also pertains to the preparation of alkyl lead compounds utilizing these novel reactive lead compositions.

Numerous processes have been proposed heretofore for the manufacture of alkyl lead compounds such as tetraethyllead and tetramethyllead. One of the most important processes for the preparation of such alkyl lead compounds involves the interaction of a sodium-lead alloy with an alkyl halide, e.g., ethyl chloride, under elevated temperature and pressure conditions.

The tetraethyllead can be separated by distillation from the reaction product mixture. Considerable effort has been expended in the preparation of special sodium-lead alloys of increased activity, since in the conventional process, as set forth above, approximately 75 percent of the lead in the sodium alloy reactant is recovered as metallic lead in the reaction product mixture. This effort has resulted in many attempts to employ finely divided sodium-lead alloys to achieve enhanced reactivity and better lead utilization. Such proposals apparently are based, in some measure, on the theory that the finely divided lead under certain conditions may also function as a halide acceptor along with the alkali metal, e.g., sodium, component of the alloy. In general, the sodiumlead alloys have been prepared by conventional metallurgical procedures followed by mechanical grinding treatment to attain the particulated sodium-lead alloys. As, is well known in the art, these processes for preparing the alloy and for subdividing the same are expensive to operate and require elaborate and costly equipment. Moreover, the mechanical grinding methods require very brittle alloys and then produce non-uniform alloy particles of varying sizes and shapes. Consequently, maximum reactivity has not been achieved.

3,558,347 Patented Jan. 26, 1971 The prior art proposals have also included the use of finely divided lead particles for reaction with alkyl halides to prepare the alkyl lead compounds. Such a method is described in US. Pat. No. 2,414,058, which issued to H. W. Pearsall on Jan. 7, 1947. The patentees contribution was to utilize the finely divided lead particles obtained from a typical sodium-lead alloy process for making alkyl lead compounds or obtained by the decomposition of tetraethyllead in a non-oxidizing atmosphere such as ethyl chloride. It is also stated that such finely divided lead particles are more reactive than mechanically divided lead. One major disadvantage of utilizing finely divided lead particles in the alkylation reaction is the absence of a highly efficient halide acceptor such as sodium or other alkali metals.

One object of the present invention is to provide an improved process for the preparation of alkyl lead compounds which avoids dilficulties and limitations encountered in the prior art processes.

Another object of the present invention is to provide an improved process for the preparation of alkyl lead compounds wherein maximum utilization of the lead reactant is achieved with attendant economic benefits.

A further object of the present invention is to provide a novel sodium-lead alkylating agent which is characterized by its outstanding reactivity and halide acceptance.

A still further object of the present invention is to provide an improved process for preparing tetraethyllead or tetramethyllead by reacting the corresponding alkyl halide with a novel sodium-lead alkylating agent.

These and other objects will become readily apparent from the ensuing description of this invention and the illustrative embodiments.

In accordance with the following invention, it has now been found that alkyl lead compounds can be elfectively prepared by reacting alkyl halides with finely divided lead particles which have been treated with an alkali metal. The preferred alkali metal is sodium, although other alkali metals such as potassium, lithium and mixtures thereof, as well as mixtures with sodium may also be utilized. The finely divided lead particles are treated with the alkali metal prior to being employed in the alkylation reaction.

The preparation of the sodium-lead compositions is accomplished according to one embodiment hereof by treating or activating finely divided lead particles with sodium or like alkali metal under such conditions that the surface of the lead particles has a sodium-lead composition, more particularly has a composition which corresponds to a sodium-lead alloy. In addition, some superficial diffusion takes place so that the composition may have an alkali metal, e.g., sodium, concentration gradient. The extent of this gradient towards the center of the particle will depend upon the ratio of alkali metal to lead which is utilized as well as upon the operating conditions, e.g., temperature and time, employed during reaction.

In a preferred composition, the sodium gradient is such that the outer portions of the particle contain sodium and lead, ideally as a sodium-lead alloy, in such proportion that the sodium content is from about 5 to about 70 percent by weight, ideally about 10 percent by weight. The very center of such particle contains little if any sodium, often being substantially free of sodium. Thus, the proportion of lead to sodium in the core of the particle is at least 30 to l and more usually is upwards of 50 to 1 approaching infinity. By virtue of the treatment or activating procedure, finely divided particulate high surface area compositions are provided which characteristically are highest in sodium (or other alkali metal) content at their surface and leanest in sodium at their core.

The finely divided lead particles, which are substantially oxide-free,-'employed= in'this invention shouldhave a diameter (or maximum dimension) particle size ranging from about 1 to 300 microns, and preferably from about 1 or to 40 microns. Although various methods of preparing the finely divided lead particles may be relied upon, and such preparation is not a basic feature of this invention, it has been found that metal spraying methods wherein the lead is atomized are particularly effective for producing the finely divided lead required in the instant process. In accordance with such a preferred method, metallic lead is atomized in an non-oxidizing atmosphere, e.g., an" inert atmosphere, such as helium, argon, nitrogen, and the like, to prevent surface and internal oxide contamination. However, other expedients such as mechanical grinding under an appropriate inert atmosphere to prevent oxidation may be used to provide lead in an appropriate state of subdivision. It is also preferred to maintain the resulting finely divided lead particles under an inert atmosphere pr'iorto use in the alkylation reactron.

It has been found that the finely divided lead particles may be effectively activated with the alkali metal by several different methods, which will be described hereinafter in terms of the preferred sodium activation.

(1) Finely divided, solid, substantially or completely oxide-free lead particles are introduced either into a stirred (or otherwise effectively agitated) reaction zone or into a fluidized bed, followed by the introduction of solid or molten sodium. An inert atmosphere is maintained throughout the treatment and during the recovery procedure. Moreover, an inert gas such as neon, argon, nitrogen and the like is employed as the fiuidizing medium when the fluidized bed technique is used. In general, the sodium either in molten or particulated solid form is slowly introduced into the reaction zone. The temperatures employed during the reaction or activation will be from about 100 C. to 300 C., and preferably from about 200 C. to 250 C., i.e., above the temperature at which the alkali metal is normally molten. Contact times Will generally be at least hour, preferably about A to 1 hour, although even longer times are of use. The amount of sodium or other alkali metal is in the range of from about 0.5 to 50 percent by weight based on the weight of the lead.

It is also possible to conduct the activation in the presence of an inert carrier. Thus, carriers in particulated form, i.e., from about 0.01 micron and upwards to 300 microns of such known inert materials as silica, alumina, talc, soda ash, sodium chloride, clay, diatomaceous earth, carbon and the like may be employed. In such a procedure, the particulate inert carrier is first added to the reaction zone, followed by the addition usually in sequence of the two reactants. In this method, the sodium may be added prior to the lead since it will coat the inert carrier particles to present a large surface area for reaction with the subsequently added finely divided lead particles.

(2) The activationof finely divided lead particles can also be accomplished in an inert liquid reaction medium. Typical liquid materials which are useful for this purpose include hydrocarbon oils, white oils, terphenyl oils, mixtures thereof and the like. In general, these inert liquid hydrocarbon oils are characteristically saturated paraflinic oils substantially free of aromatics which evidence strong chemical stability, e.g., wont discolor readily. They are typically-highly refined and have a distillation range of 700 F. to. 940 F., a specific gravity between 0.860 and 0.905 at 77 F. and a viscosity of 177 Saybolt seconds at 100 F. Either the lead (ideally in finely divided state) or the alkali metal reactant may be added first to the inert liquid with sufficient agitation or stirring to. obtain a dispersion thereof in the liquid. The other material is then added slowly while maintaining agitation. The temperature employed will range from about 100 C. to 800 C,, and preferably at least above about 150 C. Time periods are substantially the same as those used in the previously'described (1). After'sufiicient time has elapsed so as to achieve the desired degree of activation, the product mixture is used (with or without the inert liquid) as such as starting material for the preparation of alkyl lead compounds by reaction with a suitable alkyl halide.

More particularly, pursuant to one such procedure, sodium-leadcompositions are provided by first dispersing sodium or like alkali metal in a liquid medium, ideally a liquid medium such as provided by hydrocarbon oils, terphenyl oils, white oils, etc. Such sodium dispersion may be prepared by conventional techniques. Temperatures for preparing this dispersion usually are at least as high as the normal melting point of sodium, i.e., about 97.5 C., more typically in the range of C. to 250 C. Thus, the liquid medium is maintained at such a temperature while dispersing the sodium therein. In these dispersions, the sodium particle size is usually below 300 microns, ideally from 1 to 40 microns. Metallic lead, usually in molten state, and preferably as a fine stream, is added to the sodium dispersion, ideally with strong agitation. Temperatures of the dispersion to which the lead is added are above the normal melting point of lead, i.e., above about 327 C., but rarely above 800 C.

Additives which facilitate the production and stability of the dispersions often are employed. Oleic acid, aluminum stearate and like chemically dispersing agent are thus often used. Usually no more than about from 0.05 to 2.0 percent of the dispersing agent by weight is needed.

The resulting dispersion of sodium-lead particles may be directly employed in the preparation of organolead compounds, as hereinafter discussed in greater detail, or the sodium-lead may be separated from the inert liquid. These dispersions may be prepared containing up to 60 or 70 parts sodium activated lead (lead basis) per 100 parts by weight of liquid. Usually, they contain at least 10 parts (lead basis) by weight per 100 parts of the liquid.

That aspect of the present invention which relates to the activation of the finely divided lead particles will be more fully understood by reference to the following illustrative embodiments.

EXAMPLE I (A) 390 grams of finely powdered lead having an average particle size of about 40 microns were added under a helium atmosphere to a three-neck, round bottom flask fitted with a stirrer, a thermometer, a dropping tube with a side arm, and a venting tube, all of which had been previously flushed with helium atmosphere. The inert gas was introduced through the side arm of the dropping tube and withdrawn via the venting tube connected to an oil filled U tube. The lead-particles were maintained under the inert gas atmosphere during the reaction as well as duringthe recovery procedures. The reaction flask was heated until the temperature of the lead particles reached C. At-this time, 10 grams of sodium, which had been cut into inch cubes and stored under helium atmosphere, were introduced into the flask such that the temperature of reaction was not allowed to rise above C. and which was maintained between approximately 100 C. to 170 C. After all of the sodium had been added, the reaction temperature was kept at 170 C. for an additional /2 hour. After this postheating, the reaction mixture in the form of a free-flowing power was cooled to room temperature and transferred, under the helium atmosphere, to a dry box. The finely divided lead particles (about 40 microns in size) thus treated contained about 2.5 percent by weight sodium.

(B) Run Awas repeated except that the reaction temperature was maintained at about 150 C. A free-flowing powder comprising the sodium-activated finely divided lead particles having substantially the composition of the product in I(A) was recovered.

(C) Run A was repeated except that 390 grams of finely divided lead, having an average particle size of 40 microns, was reacted with 86 grams of sodium. A freeflowing powder comprising the sodium-activated lead particles was recovered containing 18 percent by weight of sodium.

EXAMPLE II 100 grams of dry silica (approximately /s inch) were placed in a three-neck, round bottom flask fitted with a stirrer, a thermometer, a dropping tube with side arms, and a venting tube. The entire system was previously flushed with helium as described in Example 1(A). The flask was heated until the temperature of the silica reached 150 C. At this time, 25 grams of sodium cut in inch cubes were introduced at such a rate that the temperature of reaction was not allowed to rise above 170 C., with the temperature ranging from about 150 C. to 170 C. After all of the sodium had been added, the temperature was dropped to 150 C., and the resulting reaction mixture was evenly sodium coated, free-flowing silica particles. Finely divided lead particles (390 grams) were then added at a slow'rate to avoid any rapid temperature rise from the heat of reaction. The temperature was not permitted to exceed 170 C., and generally was about 150 C. to 170 C. After complete addition of the lead, the resulting reaction product mixture was maintained at 170 C. for an additional /2 hour. After postheating, the flask was cooled to room temperature and the reaction product mixture of sodium-reacted lead particles was transferred under a helium atmosphere. The treated lead particles contained 6 percent sodium by weight basis their sodium-lead content.

EXAMPLE III 10 pounds of hydrocarbon oil (Primol 35 were placed in a Dispersator (a device which imparts high agitation) which had been flushed out with helium. While the flow of inert gas was continued, the Dispersator was turned on and adjusted to a speed of 2,500 r.p.m. The oil was heated to a temperature slightly below the melting point of lead, 327 C., at which time 46 grams of oleic acid was added to the reactor. 3 pounds of lead having an average particle size of 40 microns, maintained under a helium atmosphere, were introduced into the reaction zone. The speed of the Dispersator was then increased to 5,000 r.p.m. Sodium (135 grams) in the form of solid A inch cubes was next added at a rate such that the temperature of reaction was maintained between 200 C. and 250 C. After complete addition of the sodium, the temperature was maintained at 250 C. for minutes. The contents of the reactor were transferred to a storage container previously flushed with helium.

EXAMPLE IV A process as described in Example III was carried out except that the oil was heated initially above the melting point of lead, 327 C., the oleic acid was introduced, and then 3 pounds of lead as bulk lead. The speed of the Dispersator was then increased to 5,000 r.p.m. and maintained at this speed. Once all the lead was dispersed, i.e., 5 minutes, the temperature was dropped below the melting point of lead, 327 C., i.e., to 200 C. Then the sodium addition and reaction was conducted as in Example III.

EXAMPLE V The procedure of Example III was followed except that 6 pounds of the finely divided lead was used.

EXAMPLE VI To 10 pounds of hydrocarbon oil (Humbles' Primol 355) in a Dispersator, 135 grams of sodium is added at a temperature of 150 C. while operating the Dispersator as described in Example III. After 30 minutes, the sodium particle size is about 10 microns. The temperature of the resulting sodium dispersion is then raised to 330 C. and 3 pounds of lead in the formof a fine stream is injected intothe dispersion while the Dispersator is operating and 6 agitating the dispersion. A dispersion in Primol 355 of sodium-lead particles below microns in size is thus produced.

The above data demonstrate that a number of special methods may be employed to prepare the sodium-reacted lead particles of this invention.

As previously discussed, the sodium-reacted lead particles of this invention are particularly useful for the preparation of organolead compounds, especially alkyl lead compounds, most notably tetraethyllead and tetramethyllead. The starting materials are alkyl halides, wherein the alkyl group contains from about 1 to 2 carbon atoms. The use of alkyl chlorides is preferable, although the bromides and iodides may also be utilized. Specific starting materials include the following:

methyl chloride methyl bromide methyl iodide ethyl chloride ethyl bromide ethyl iodide Other alkyl as well as aralkyl halides are also capable of being converted by the sodium-lead composition to organolead compounds.

In general, the reaction between sodium treated lead particles of this invention and the alkyl halide is carried out at a temperature within the range of about 35 C. to 160 C., preferably about 90 C. to 100 C., and at a pressure suflicient to maintain the alkyl halide in the liquid state. It is beneficial that a stoichiometric excess of at least 50 percent of the alkylating agent, i.e., the alkyl.

40 pounds from the solids present in the reaction product mixture by filtration or centrifugation and to recover any unreacted lead particles or by-product lead, It will be further understood that other separation techniques, including'decantation of the liquid reaction products and steam distillation of the liquid reaction products, may be employed to recover the desired alkyl lead compounds.

As is well known in the art, it can be advantageous to employ an accelerator when the sodium-activated lead particles of this invention are reacted with the lower alkyl halides. Other minor proportions, i.e., about 0.01 to 0.5 percent by weight based on the weight of the alkyl halides fed, need be employed. An illustrative accelerator is acetone.

The alkylation process of this invention will be more fully understood by reference to the following illustrative embodiments.

EXAMPLE VII 11.5 grams of the sodium-reacted lead particles (containing 2 /2 percent sodium) prepared by the method of Example I(A) were charged to a reaction bomb under a helium atmosphere. 34 milliliters of ethyl chloride and 0.03 milliliter of acetone were then added. The bomb was sealed and heated in an oil bath to C. for 1% hours While agitating the reaction mixture. The resulting reaction product mixture was cooled to room temperature, removed from the bomb, and analyzed as follows:

' Grams Residual lead 6.082 Lead chloride 1.62 Tetraethyllead 2.00

EXAMPLE VIII 11.5 grams of sodium-reacted lead particles having an average particle size of about 40 microns and a sodium content of 10 percent by weight, prepared in accordance with the method of Example I(A), were charged to a reaction bomb under a helium atmosphere. 35 milliliters of ethyl chloride and 0.03 milliliter of acetone were then added, and the bomb was sealed and heated in an oil bath to 120 C. for 1 hour. Agitation was maintained throughout the reaction period. After being cooled to room temperature, the resulting reaction product was removed from the bomb and analyzed:

Grams Residual lead 2.08

Lead chloride 5.6

Tetraethyllead 6.56

EXAMPLE IX (A) 11.5 grams of the sodium-reacted lead particles having an average particle size of 40 microns and a sodium content of 18.5 percent by weight, prepared in accordance with the method of Example I(A), were charged to a reaction bomb under a helium atmosphere. 35 milliliters of ethyl chloride and 0.03 milliliter of acetone were added, the bomb was sealed and then heated in an oil bath to 120 C. for 1 hour. Agitation was maintained during the reaction. After the resulting reaction product mixture was cooled to room temperature, it was removed from the bomb and analyzed:

Grams Residual lead 4.7 Tetraethyllead 7.4

(B) Run (A) was repeated except that sodium-reacted lead particles had a sodium content of 31.2 percent by weight. The reaction product mixture contained 12.4 grams of tetraethyllead.

EXAMPLE X (A) 13.7 grams of the sodium-reacted lead particles in a mixture with silica, prepared in accordance with the method of Example II, were charged to a reaction bomb under a helium atmosphere. 35 milliliters of ethyl chloride and 0.03 milliliter acetone were then added to the bomb, the bomb was sealed and heated to 120 C. in an oil bath for 1 hour. The reaction mixture was subjected to continuous agitation during this period. After cooling the resulting reaction product mixture to room temperature, it was removed from the bomb and analyzed:

Grams Residual lead 6.17 Lead chloride 2.74 Tetraethyllead 4.06

(B) Run (A) was repeated except that 46.2 grams of the sodium-reacted lead particles, prepared in accordance with Example III, was employed. The resulting reaction product mixture contained 4.06 grams of tetraethyllead and 7.7 grams of residual lead.

It is possible to prepare alkyl lead compounds from dispersions of sodium-activated lead particles which are prepared according to Examples III, IV, V and VI without removing the hydrocarbon oil or part of the oil. That is, the dispersion may be directly used in the preparation or may have either a part or all of the oil removed. This is illustrated in the following example:

EXAMPLE XI A dispersion in Primol 355 of a sodium-reacted lead containing about 10 weight percent sodium prepared according to the general procedure of Example VI was allowed to stand and the supernatent oil decanted. Some 46 grams of the residue (about by weight 52 percent NaPb and 48 percent Primol) was charged along with 100 milliliters of ethyl chloride and 0.29 milliliter of acetone to a reactor which was then sealed and placed in an oil bath at 100 C. After 1 hour, the reactor was cooled, opened and the contents extracted. Analysis of the extract showed high conversions of the NaPb to tetraethyllead.

The above data show that the sodium-activated lead particles of this invention can be effectively employed 5 to prepare valuable alkyl lead compounds from lower alkyl halides. It has also been demonstated that the sodium-reacted lead particles may be readily prepared without the costly equipment and operational procedures of the prior art teachings concerning the formation of more reactive lead materials and their use in alkylation reactions.

While particular embodiments of this invention are shown above, it will be understood that the invention is obviously subject to variations and modifications without departing from its broad aspects. Thus, for example, the preparation of the sodium-reacted lead particles and the alkylation reaction may be readily conducted in a continuous manner.

What is claimed is:

1. A process for preparing highly reactive lead alloy particles having a high concentration of alkali metal on the surface of the particle and a lower alkali metal content below said surface comprising contacting finelydivided lead particles having an average particle size 25 within the range of 1 to 300 microns with alkali metal at temperatures above that at which the alkali metal is molten and in an inert gaseous atmosphere to thereby alloy the lead particles and the alkali metal and produce the said highly reactive lead alloy particles.

2. The process of claim 1 wherein said alkali metal is sodium.

3. The process of claim 1 wherein said lead particles have an average particle size within the range of about 1 to 40 microns.

4. The process of claim 1 wherein the finely divided lead particles and the alkali metal are contacted in the presence of an inert, finely divided, solid material.

5. The process of claim 4 wherein said inert solid material is silica.

40 6. The process of claim 1 wherein the finely divided lead particles and the alkali metal are contacted in the presence of an inert liquid material.

7. The process of claim 6 wherein said inert liquid material is a hydrocarbon oil.

8. A process for preparing highly reactive lead alloy particles which comprises contacting finely-divided lead particles having an average particle size of l to 40 microns with alkali metal at temperatures within the range of about 100 C. to 300 C. in an inert gas atmosphere for a period of time sufficient to alloy the particles with the alkali metal to thereby produce substantially oxidefree particles having their surfaces coated with an alloy of alkali metal and lead and having an alkali metal-lead mixture below their surface having a lower alkali metal content than the surface coating and recovering the particles so coated.

9. The process of claim 8 wherein said alkali metal WILLIAM D. MARTIN, Primary Examiner M. R. P. PERRONE, Jr., Assistant Examiner U.S. Cl. X.R. ll7118, 131 

